1. Field of the Invention
The present invention relates to powered ophthalmic lenses, and more particularly to wireless communication protocols for use in conjunction with powered ophthalmic lenses or other devices that are extremely small and energy limited.
2. Discussion of the Related Art
As electronic devices continue to be miniaturized, it is becoming increasingly more likely to create wearable or embeddable microelectronic devices for a variety of uses. Such uses may include monitoring aspects of body chemistry, administering controlled dosages of medications or therapeutic agents via various mechanisms, including automatically, in response to measurements, or in response to external control signals, and augmenting the performance of organs or tissues. Examples of such devices include glucose infusion pumps, pacemakers, defibrillators, ventricular assist devices and neurostimulators. A new, particularly useful field of application is in ophthalmic wearable lenses and contact lenses. For example, a wearable lens may incorporate a lens assembly having an electronically adjustable focus to augment or enhance performance of the eye. In another example, either with or without adjustable focus, a wearable contact lens may incorporate electronic sensors to detect concentrations of particular chemicals in the precorneal (tear) film. The use of embedded electronics in a lens assembly introduces a potential requirement for communication with the electronics, for a method of powering and/or re-energizing the electronics, for interconnecting the electronics, for internal and external sensing and/or monitoring, and for control of the electronics and the overall function of the lens.
The human eye has the ability to discern millions of colors, the ability to adjust easily to shifting light conditions, and transmit signals or information to the brain at a rate exceeding that of a high speed internet connection. Lenses, such as contact lenses and intraocular lenses, currently are utilized to correct vision defects such as myopia, hyperopia and astigmatism. However, properly designed lenses incorporating additional components may be utilized to enhance vision as well as to correct vision defects.
Conventional contact lenses are polymeric structures with specific shapes to correct various vision problems as briefly set forth above. To achieve enhanced functionality, various circuits and components have to be integrated into these polymeric structures. For example, control circuits, microprocessors, communication devices, power supplies, sensors, actuators, light emitting diodes, and miniature antennas may be integrated into contact lenses via custom built optoelectronic components to not only correct vision, but to enhance vision as well as provide additional functionality as is explained herein. Electronic and/or powered contract lenses may be designed to provide enhanced vision via zoom-in and zoom-out capabilities or just simply modifying the refractive capabilities of the lenses. Electronic and/or powered contact lenses may be designed to enhance color and resolution, to display textural information, to translate speech into captions in real time, to offer visual cues from a navigation system, to provide image processing and internet access. The lenses may be designed to allow the wearer to see in low light conditions. The properly designed electronics and/or arrangement of electronics on lenses may allow for projecting an image onto the retina, for example, without a variable focus optic lens, provide novelty image displays and even provide wakeup alerts. Alternately, or in addition to any of these functions or similar functions, the contact lenses may incorporate components for the noninvasive monitoring of the wearer's biomarkers and health indicators. For example, sensors built into the lenses may allow a diabetic patient to keep tabs on blood sugar levels by analyzing components of the tear film without the need for drawing blood. In addition, an appropriately configured lens may incorporate sensors for monitoring cholesterol, sodium and potassium levels as well as other biological markers. This coupled with a wireless data transmitter could allow a physician to have almost immediate access to a patient's blood chemistry without the need for the patient to waste time getting to a laboratory and having blood drawn. In addition, sensors built into the lenses may be utilized to detect light incident on the eye to compensate for ambient light conditions or for use in determining blink patterns.
The proper combination of devices could yield potentially unlimited functionality; however, there are a number of difficulties associated with the incorporation of extra components on a piece of optical grade polymer. In general, it is difficult to manufacture such components directly on the lens for a number of reasons, as well as mounting and interconnecting planar devices on a non-planar surface. It is also difficult to manufacture to scale. The components to be placed on or in the lens need to be miniaturized and integrated onto just 1.5 square centimeters of a transparent polymer while protecting the components from the liquid environment on the eye. It is also difficult to make a contact lens comfortable and safe for the wearer with the added thickness of additional components.
Communication with a powered ophthalmic device offers a number of unique challenges. Wireless communication protocols provide a structure for transmitting data or information in an organized way to facilitate efficient operation of either or both the transmitter and receiver. Aspects of the data transmission determined by the protocol comprise the method of transmission, for example, modulating a carrier signal, the modulation format, the structure of the data messages, and additional data sent to facilitate synchronization of the receiver to the transmitter as well as error correction at the receiver.
Prior art protocols for radio frequency (RF) or infrared (IR) communication are commonly used for data communication utilizing digital modulation formats such as amplitude-shift keying (ASK), on-off keying (OOK), phase-shift keying (PSK) or frequency-shift keying (FSK) as are well known in the relevant art. These protocols may be utilized for communication between fixed transmitters and receivers as well as between mobile or portable transmitters or receivers.
In particular, portable transmitters and receivers impose design constraints on power consumption due to the limited capacity of the batteries utilized to power the transmit and receive circuitry. In order to reduce power consumption, prior art protocols allow for intermittent transmission and reception by sending data from the transmitter only when needed rather than by requiring the continuous transmission of the carrier signal. The receiver may conserve power by periodically turning on (waking-up or strobing) and searching for a transmission.
Prior art protocols fall into two categories; namely, asynchronous and synchronous. In asynchronous protocols, the receiver searches for a transmission and then synchronizes to the transmitted data stream to decode the transmitted message. In synchronous protocols, the receiver maintains a time reference that is synchronized to the transmitter time reference, often after a successful asynchronous reception. Accordingly, certain prior art protocols provide for asynchronous operation initially followed by synchronous operation for later reception intervals.
In asynchronous operation, in order to properly receive the data, the receiver must understand where the start of the data transmission begins. In prior art protocols, the transmitter first sends a long preamble usually comprising a simple one and zero data pattern followed by a synchronization word and then the data. The preamble is at least as long as the receiver wake-up or strobe interval to ensure that the receiver will always see the preamble. The Post Office Code Standardization Advisory Group (POCSAG) protocol is an example of this type of asynchronous protocol. It is utilized to transmit information or data to pagers.
Prior art protocols thereby reduce both receiver and transmitter power consumption by this method of intermittent transmission and reception. These protocols are particularly effective in reducing transmitter power consumption which is important for battery powered hand held remote controls and small wireless sensor transceivers.
However, in the case of extremely small and/or energy limited receivers, the prior art communication protocols have a number of drawbacks. For example, when a preamble is detected, the receiver must remain on for, on average, over half the length of the preamble or strobe interval to wait for the transmit synchronization word and data. For many systems, the length of the data transmission may be significantly shorter than the strobe interval which means the wait period represents significant overhead. Also, small batteries tend to have high series resistance, and the receiver current may be high enough to induce a significant voltage drop at the battery. To compensate, additional decoupling capacitance may be added to provide a charge reservoir to reduce the voltage drop, with a resulting tradeoff of an increased cost, increased complexity, and higher area and volume receiver. Finally, very low power systems tend to implement very simple modulation methods such as ASK or OOK to reduce the complexity and power consumption of the receiver. These amplitude modulation detectors are likely to falsely detect a one-zero preamble pattern from noise on the transmission channel, leading to longer receiver “on” times when no transmission is actually occurring.
Synchronous protocols provide some advantages over asynchronous protocols because the long preamble of an asynchronous protocol need not be decoded by the receiver. Once synchronized, the receiver can turn on or wakeup just prior to the transmit synchronization word thereby reducing the receiver on time. However, in order to have long sleep or off periods, the receiver and transmitter must retain accurate time bases with little or no drift over time and with little changes over environmental conditions. This typically requires the use of a ceramic resonator or quartz crystal-based oscillator which increases the size, cost and current consumption of the receiver.
Accordingly, there exists a need for a wireless communication protocol that enables the use of extremely low power consumption and extremely small size or volume receivers by minimizing the required receiver on-times.